This invention concerns immunoassay methods for the detection or measurement of substances in liquid samples, e.g., biological fluids such as whole blood, serum, plasma, and urine.
A wide variety of substances are commonly detected or measured by immunoassay methods, for example, hormones, antibodies, toxins, drugs, and antigens such as viral particles. Usually, although not always, either the substance being detected or a substance used in its detection is an antibody, hence the term "immunoassay." The antibody is a member of a specific binding pair, the other member of the pair being referred to as an antigen, or analyte. Other specific binding pairs, besides antibodies-antigen pairs, which are measured and used in similar assays, include pairs of molecules which have specific binding affinity for each other, e.g., hormones and hormone receptors, and biotin and avidin.
Immunoassays are commonly carried out, at least in part, on solid supports, e.g., glass fiber membranes. The two most common formats for immunoassays employing solid supports are competitive and sandwich formats. Typical competitive formats are described e.g., in Littman et al., U.S. Pat. No. 4,540,659, and a typical sandwich assay by David et al., U.S. Pat. No. 4,376,110.
Examples of the use of a sandwich test are an immunofluorescent assay (IFA) and an enzyme-linked immunosorbent assay (ELISA). Both these assays are used for detection of a common disease of cats, feline leukemia virus (FeLV).
FeLVs are an endogenously replicating C-type oncornavirus; the viral genome is incorporated into the host chromosome as a provirus, and the genome is translated to produce intact virions. The virus is spread horizontally from infected to susceptible cats and causes a number of disease syndromes ranging from myeloid and lymphoreticular neoplasms to an acquired immunodeficiency syndrome.
Another virus which infects cats is a retrovirus recently isolated from a group of cats suffering from immunodeficiency-like syndrome; the virus is termed feline-T-lymphotrophic lentivirus (FTLV or FIV). It belongs to the same group as the human immunodeficiency virus (HIV), the causitive agent of human AIDS. FIV is described by Pederson et al., 235 Science 790, 1987. Antibody to FIV has been detected by use of an IFA.